Country star Carrie Underwood has been dragged into another plagiarism spat over her Sunday Night Football theme song Game On.

Heidi Merrill, who enjoyed success with sports themed Cornhusker Strong in 2015, has filed suit against the singer, accusing her of recording a song she passed on to the Jesus Take the Wheel hitmaker's producer without permission.

In legal papers obtained by TMZ, Merrill claims she offered her version of Game On to Carrie's producer, Mark Bright, at an event in Nashville, Tennessee, in August, 2017 and asked him if the former American Idol star would be interested in recording it.

Bright was initially interested but eventually told Merrill that Carrie had passed on the track.

Merrill says she was shocked when Underwood first performed her new Sunday Night Football theme, also called Game On, and now insists it's not just the title that's similar, and she is suing Carrie, Bright, bosses at TV network NBC, and the National Football League for copyright infringement.

Carrie was also recently accused of stealing her hit Something in the Water from songwriters Ron McNeill and Georgia Lyons.

They claim they originally wrote the track but received no credit.

Underwood's publicist has shot down their claims, insisting Something in the Water is "deeply personal" for the singer.

"We are aware that a lawsuit was filed regarding the authorship of Something in the Water (and) we want all of Carrie’s fans, and everyone, to know that Something in the Water was written by Brett James, Chris DeStefano, and Carrie Underwood," she said. "This is a deeply personal song regarding Carrie’s faith and she is saddened that anyone would attempt to challenge that for financial gain. Neither Carrie nor any of her co-writers ever received or heard the plaintiffs’ song. We fully expect that Carrie, Brett, and Chris will be vindicated in the courts."